Help! I want to show picture on the Video.

Title: Help! I want to show picture on the Video.

I use QT to show picture, V4L2 to show video.

I know to use alpha blending to show picture.

    set_video_fmt( 720, 480 );
    capture_enable(1);
    set_overlay_info( OVERLAY_KEY, OVERLAY_MASK, 1, 1 );
    set_alpha_blend_info( 0, 0, 0, 720, 480, 1, 0, 0, 1, 0xFFFF0000 );
    set_vout_window( 0, 0, 720, 480 );
    set_input(1);
    preview(1); // show video
    set_alpha_blend_info( 1, 550, 50, 120, 120, 1, 180, 0, 1, 0xFFFF0000 ); //to show picture

If I don't use alpha window to show picture, I want to show picture on video overlay.
How can I do?